In TinyMCE 4 you can provide CSS classes for images, then the image dialog provides a select box to choose from, and the CSS classes can be assigned to the image. These CSS classes can be grouped. The CSS classes must be defined in the stylesheet.css of the template.

The code block image_class_list you also can add to other ini-files. But these files could be overwritten during an update. Therefore it is always the better way for individual changes, to copy an existing init file, rename it (maybe init_customized.js), and then edit and activate the customized init-file.